filter: Replace '.' in counter names with ':'

The '.' is illegal character in counter names, as they are exported
via CTRL interface, where '.' has a special meaning that cannot be
used by strings comprising the variable name.

Forward-port from openbsc.git 360284d4d797519faed33559b0ae746b6c17e68a.

Change-Id: I57b78162701a6a101b5cbaf68aaea89d17a0f819
1 file changed